Heart Pin

Heart Pins (or more precisely, Clover Leaves) are the things the main characters all wear on the right side of their chest. When combined, they make a 4 leaf clover, which is the logo for the series.

these things can be taken of a ghost and can fuse it with a mortal or a person that has not died yet. Fusing all 3 create a clover that can with its spritual powers can open doors that lead to a mortals body and let them continue their life on where they left off.

it is unkown if ghost can go inside their pins and affect the power within them, if not then george, brenda and dave either went to heavan or got back to their resting places. If so then they had probably fused all their souls to fill out the broken peices kel had and sacrificed their souls to let hers continue to live.

The amulet Kel holds in her hand is maybe what gives this lucky energy and is a heirloom to her family as they pass it on to each generation.

Trivia

 * The clovers on their chest Heavily imply that they are the things that let the ghost see each other, and see kel, who is rather in a near death experience rather then fully dead. (Or they are all family which would make much better sense rather then strange ghosts, and making George, Brenda, and Dave all Kel's ancestors.)
 * George, Brenda, and Dave have normal clover leaves, meaning they have died naturally. On the other hand. Kel has a broken clover leaf. Meaning she may have forced death on herself. or another idea may be that the hearts pinned on their shirts are their state right now, Kel is depressed, hence her "heart" being broken since she hasn't come to terms with her inner ghosts (pun intended) while the ghosts' hearts are whole because they have accepted their lives (or past lives), moving on, and now they're helping Kel do the same. Based on a comment made by Darshi Patel.
 * It is implied (or it is a fact) that George is the ghost of the past (overcoming the loss of his loved one). Brenda is the ghost of the present (overcoming the present disease that was infecting her ability to dance). Dave is the ghost of the future (looking forward to making wubby a sucess in cinematic history, no matter the circumstances.)